1. Field of the Invention
The present invention relates to a force sensor that detects external force and a robot arm including the force sensor.
2. Description of the Related Art
In these years, as robotics develops, there is a growing trend toward use of vertical articulated robots that automatically operate in accordance with control programs for manufacture of products. In order to manufacture products for which precise assembly operations are required, a robot including a force sensor has been proposed whose robot arm includes, at a position corresponding to a wrist portion of the robot arm, a force sensor for detecting external force and that is capable of performing precise assembly operations while detecting external force applied to a robot hand connected to the robot arm.
As the force sensor for detecting external force, a force sensor of a magnetic type is known (Japanese Patent Laid-Open No. 2009-75083). The force sensor of a magnetic type has a structure in which magnetic flux generating sources and magnetoelectric transducers are held in such a way as to be able to move relative to each other. The output voltages of the magnetic flux generating sources change in accordance with the magnetic flux density of magnetic flux flowing to the magnetoelectric transducers, which changes in accordance with a distance between the magnetic flux generating sources and the magnetoelectric transducers that may be changed by external force. By detecting the output voltages, the magnitude of the external force may be detected.
On the other hand, a device called a “slip ring” that is capable of transmitting electric power and electrical signals from a stationary body to a rotating body is known (Japanese Patent Laid-Open No. 06-310250). The slip ring is used when electric power and data signals are to be transmitted in an electromechanical system that needs to intermittently or continuously rotate. By providing the slip ring at a rotating unit instead of providing a transmission cable that is easily broken due to metal fatigue caused by bending at the rotating unit, the performance of the system improves and the operation of the system may be simplified. In the case of a robot, wires that are easily broken at movable joints may be omitted. The slip ring is also called a “rotary electrical joint” or a “collector”, but will be simply referred to as the slip ring hereinafter. Although apparatuses capable of transmitting electric power and electrical signals from a stationary body to a rotating body include a rotary connector that utilizes conducting fluid, the rotary connector will also be referred to as the “slip ring” in the following description. Members that rotate relative to each other such as a brush and rings in the slip ring may be referred to as a stationary body and a rotating body for the sake of convenience.
A robot is normally fixed to a base. A fixed end of the robot is configured by a thick, large member because the fixed end of the robot needs to be firmly fixed physically. On the other hand, compared to the fixed end, an arm of the robot (robot arm) is designed to become thinner and thinner on the side of a free end, so that a wide movable range is secured and various attitudes necessary to perform operations are established while avoiding collisions. Therefore, at positions close to the free end of the robot arm, there are limitations in design, that is, the area of regions other than links and joint portions of the robot arm in which additional components may be mounted is small.
When a slip ring is to be mounted on a wrist portion located close to the free end of a robot arm of an articulated robot in addition to a force sensor in order to transmit electrical signals and supply power, the force sensor and the slip ring are to be individually provided, which undesirably increases the required mounting volume in the wrist portion.
The present invention provides a force sensor that may be suitably mounted on a rotating unit of a robot arm and that is capable of supplying power, detecting external force, and reducing the mounting volume.
Furthermore, the present invention provides a robot arm including the force sensor.